The invention relates to the connection of an anchor rod to a drilling tool of a device for setting of self-drilling injection bolts.
In order to be able to install self-drilling injection bolts in rock, it is necessary for the anchor rods comprising the bolt system to be connected to the drilling head of a drilling tool. The connection is made via a transition sleeve into which one end of the anchor rod is screwed and which is coupled to the insertion end of the drilling tool, for example, by screwing on. A drill bit is screwed on the frontmost end of the first anchor rod. As the depth of the bore hole progresses the anchor rod is lengthened by screwing on connecting couplings and other anchor rods until the total bolt length is reached. When an anchor rod is used, it is necessary to break the connection between the last anchor rod which has been drilled in the rock and the drilling tool by the last anchor rod which is projecting out of the bore hole being screwed out on the transition sleeve and a new anchor rod being inserted, and the latter must be lengthened with the last anchor rod by a connecting coupling and must be screwed into the transition sleeve of the drilling tool.
The release first of the anchor rod from the transition sleeve on the drilling tool proved to be a problem in the prior art. In the known execution of the ends of the anchor rods it often happens that the anchor rod sticks in the transition sleeve which connects it to the drilling tool; this leads to disruptions in operation since considerable force and time are necessary to break the screw connection between the anchor rod and the transition sleeve. The reason for the sticking which often occurs is that anchor rods which have not been heat treated compared to drill collars which are always used in tempered quality have low hardness. The transition sleeve of the drilling tool, which sleeve is likewise always tempered, since it is designed for repeated use, is much harder than the anchor rods. During operation, therefore while drilling, residual deformation of the end of the anchor rod held in the transition sleeve is caused by the process of rotary percussive drilling (rotary motion and percussive motion), by which the aforementioned problem of sticking of anchor rods in the transition sleeve arises.
U.S. Pat. No. 4,332,502 A discloses forming unthreaded sections on the ends of anchor rods for anchor rods which are to be connected to one another by connecting couplings. The anchor rods are connected to one another in U.S. Pat. No. 4,332,502 A by connecting couplings which, in the area in which the anchor rods which have been screwed into the connecting couplings, adjoin one another with their unthreaded sections, have a ring which projects to the inside and into which the unthreaded ends of the anchor rods which have been screwed into the transition sleeve fit. This means that in the case of percussive loads on the anchor rods as occurs in the setting of roof bolts, when bore holes are produced with them, deformations will occur mainly in the area of the adjoining ends, therefore in the area of the unthreaded sections of the anchor rods so that the unthreaded sections of the anchor rods are flattened and mushroomed as their diameter increases. These deformations will result in that the sticking between the anchor rods and the sleeve which was considered disadvantageous above will occur.